car alternator?

my car shows battery warning when driving at night. one time i drove to buy stuffs at the town, battery warning glowed and the steering went a little heavy. and so i went on, parked my car, and went to buy things. when i went back to the car, it wont start and started to produce ticking sounds. i called my mechanic but he was out of town but instructed me to get my car pulled to his shop and so i did. i went there the next day and he said either the battery is dead due to old age, or there's something wrong with the alternator. he's not an electrician. he's a mechanic. hope you can help me. thanks guys, and more power!